Locking Device

ABSTRACT

The invention relates to a locking device to radially lock a rotatable cylindrical element, where the locking device ( 1 ) comprises a roller element ( 2 ) and at least a first inclined surface ( 3 ). The locking device is arranged to be positioned in relation to a cylindrical surface ( 13 ) around the cylindrical element ( 12 ) in such a way that the distance between a starting point ( 10 ) of the first inclined surface ( 3 ) and the cylindrical surface ( 13 ) is larger than the diameter of the roller element ( 2 ) and that the distance between an end point ( 11 ) of the first inclined surface ( 3 ) and the cylindrical surface ( 13 ) is smaller than the diameter of the roller element ( 2 ). The locking device further comprises means ( 6 ) to selectively enable the roller element ( 2 ) to be distanced from the cylindrical surface ( 13 ). The advantage of the invention is that a locking device can be obtained in an easy and cost-effective way.

TECHNICAL FIELD

The present invention relates to a locking device for radially locking arotatable cylindrical element, such as an axle.

BACKGROUND ART

Linear actuators are used to move an object along a straight line,either between two end points or to a defined position. Some linearactuators are driven by electricity.

Electrically driven linear actuators normally incorporate a rotatingmotor and some kind of transmission means to convert the relativelyhigh-speed rotating motor to a low speed linear motion. Thistransmission means may incorporate a gear box and/or a screw shaft. Onecommon type of linear actuator incorporates a screw shaft with a nutrunning thereon. The screw shaft extends over the full length of theactuator and sets the operating length of the actuator. Since the nut isheld in a non-rotatable state, the nut will be displaced when the screwshaft is rotated by a motor. The nut may incorporate rolling elements,such as balls or rollers, between the screw shaft and the nut. This willallow for a high efficiency actuator with high load transfer and longlife. The nut may also engage directly with the screw shaft, i.e. asliding screw design. In this case, the nut is preferably made of aplastic material.

Depending on the type of linear actuator and the gear ratio in theactuator, the motor may be self-locking, i.e. an external force appliedto the actuator will not rotate the motor when the motor is not powered.One example of a self-locking linear actuator is the type using asliding nut or screw; another type uses a motor with a high ratio gearbox. In these types, the force applied on the linear actuator will notbe able to rotate the motor since the gear ratio will step up theholding force of the motor with the gear ratio factor. Internal frictionin the sliding screw or nut will also provide a holding force.

Linear actuators using a ball or roller screw are sometimes notself-locking, depending on the low internal friction. Such linearactuators may comprise some kind of locking means in order to hold thelinear actuator in a required position. The locking means may e.g. be afriction brake of some kind, e.g. a disc brake acting on a separatebrake disc or a brake pad acting on the motor or linear actuatordirectly. In one type of brake, the brake pad is forced into brakingaction by a power means, e.g. an electromagnet pushing or pulling thebrake pad to the brake surface. In another type of brake, the brake padis applied with a spring and then released from the braking action by apower means, e.g. an electromagnet pushing or pulling the brake pad fromthe brake surface.

It is also possible to apply a voltage to the motor in order to hold theposition of the motor, even though this method should only be used forshort periods due to heat generated in the motor.

All these brake devices require rather substantial power consumption inorder to hold at least one of the brake states, i.e. applied brake ornon-applied brake. There is thus room for improvements.

DISCLOSURE OF INVENTION

An object of the invention is therefore to provide a locking device thatrequires low power to engage and that is easy and cost-effective toproduce.

With a locking device for radially locking a rotatable cylindricalelement in a first direction of rotation, where the locking devicecomprises a roller element and at least a first inclined surface andwhere the locking device is arranged to be positioned in relation to acylindrical surface around the cylindrical element in such a way thatthe distance between a starting point of the first inclined surface andthe axle surface is larger than the diameter of the roller element andthat the distance between an end point of the first inclined surface andthe axle surface is smaller than the diameter of the roller element, theobject of the invention is achieved in that the locking device comprisesmeans to selectively enable the roller element to be distanced from thecylindrical surface.

To enable radial locking of the cylindrical element in a seconddirection of rotation, the locking device preferably comprises a secondinclined surface. The second inclined surface is suitably positionedopposite from the first inclined surface relative to a radial centrelineof the device and is likewise positioned such that the distance betweena starting point of the second inclined surface and the axle surface islarger than the diameter of the roller element and that the distancebetween an end point of the second inclined surface and the axle surfaceis smaller than the diameter of the roller element.

Thus, a locking device is provided which can radially lock a rotatablecylindrical element in a clockwise and a counter-clockwise direction.The device is, moreover, self-locking and requires low power to engageand disengage. The locking device can take up a high locking force, andthe locking action will increase when a higher force is applied. Thelocking device is further relatively easy and cost-effective to produce,since it contains few parts. This is advantageous in that a lockingdevice that is compact can be obtained.

The means to selectively enable the roller element to be distanced fromthe cylindrical may be a lifting device. In an advantageous developmentof the invention, the lifting device is activated to lift the rollerelement from the cylindrical surface in order to place the lockingdevice in a released state. In the context of this patent specification,the verb ‘lift’ is understood to mean any distancing action that causesthe roller element to be released from the cylindrical surface. Bylifting the roller element from the cylindrical surface, the cylindricalelement can rotate freely in any direction. Since the power required tolift the roller element is relatively low, a disengageable lockingdevice with low energy consumption is obtained.

In an advantageous development of the invention, the lifting device is amagnet. This allows the roller element to be lifted in a contactlessmanner. The advantage of this is that the locking device can be shieldedin order to improve reliability. The lifting device is in one embodimentan electromagnet. By using an electromagnet, the engagement anddisengagement of the lifting device is improved. Another advantage ofusing an electromagnet is that the induction of the coil of theelectromagnet can be measured. This makes it possible to detect if aroller element is actually being lifted by the lifting device or not.This will improve the reliability of the locking device.

In another advantageous development of the invention, the locking devicecomprises a spring element to force the roller element towards thecylindrical surface when the lifting device is disengaged. This allowsfor the locking device to be mounted in any required position. When thelocking device comprises such a spring element, the lifting power of thelifting device additionally acts to overcome the force exerted on theroller element by the spring element, so that the roller element can belifted from the cylindrical surface. In the case where the inclinedsurface or surfaces and the lifting device are positioned at “sixo'clock”, the lifting device need only overcome the spring force, asgravity will cause the roller element to be released from thecylindrical surface.

In an advantageous further development of the invention, the inclinedsurfaces are symmetrical around a radial centreline of the lockingdevice. By using symmetrical inclined surfaces, the locking action willbe the same regardless of which locking direction is used.

In an advantageous further development of the invention, the lockingdevice comprises means to detect when the roller element is in a liftedstate. By doing this, it is possible to detect that the locking deviceis actually in a released state. This is advantageous in that the actualstate of the locking device can be detected. If e.g. the lifting devicemalfunctions or the roller element sticks to the inclined surface, theroller element may not be lifted even though a signal is sent toactivate the lifting device. The reliability of the locking device isthus further improved.

In an advantageous further development of the invention, the lockingdevice comprises means to detect if the locking device is in a first orsecond locked state. By doing this, it is possible to detect in whichrotational direction the cylindrical element was rotating when thelocking device was activated. This makes it possible to decide in whichdirection the cylindrical element is to be rotated in order to releasethe cylindrical element and thus to place the locking device in areleased state. Rotating the cylindrical element in the wrong directionmay damage the locking device or the device driven by the cylindricalelement. The reliability of the locking device is thus further improved.

In an advantageous further development of the invention, the cylindricalelement of the locking device comprises a tubular element and a frictioncoupling. This reduces the risk of overloading the locking device, andat the same time allows the use of the locking device as an emergencybrake. The friction coupling can be set to slip at a predefined force.

In an advantageous further development of the invention, the lockingdevice comprises a second roller element, two further inclined surfacesand a second lifting device. This allows a symmetric load on the axleelement which is advantageous in that the wear of the mechanical systemis reduced.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be described in greater detail in the following, withreference to the embodiments that are shown in the attached drawings, inwhich

FIG. 1 shows the geometry of an embodiment, in a frontal view, of alocking device according to the invention,

FIG. 2 shows a first embodiment of a locking device according to theinvention in a released state,

FIG. 3 shows the first embodiment of a locking device according to theinvention in an engaged state,

FIG. 4 shows the first embodiment of a locking device according to theinvention in a locked state,

FIG. 5 shows a second embodiment of the locking device according to theinvention in an engaged state, and

FIG. 6 shows the second embodiment of the locking device according tothe invention in a locked state.

MODES FOR CARRYING OUT THE INVENTION

The embodiments of the invention with further developments described inthe following are to be regarded only as examples and are in no way tolimit the scope of the protection provided by the patent claims. FIG. 1shows the geometry of a first embodiment of a locking device accordingto the invention. FIGS. 2 to 4 show the same locking device, where thelocking device is in a released, an engaged and a locked state,respectively. The locking device 1 comprises a roller element 2, a firstinclined surface 3 and a second inclined surface 4. The locking devicefurther comprises a spring element 5 and a lifting device 6.

The locking device is adapted to be mounted on a mechanical devicecomprising a rotatable cylindrical element 12, such as an axle, a hollowaxle, a tubular element or the like. The mechanical device may e.g. be amotor, a transmission device, a linear actuator or the like.

In one embodiment, the roller element is completely round, i.e. a ball.In another embodiment, the roller element is a cylinder with apredefined length and a diameter d. The roller element is preferablymanufactured in a hard material, e.g. hardened steel, in order to beable to handle the imposed loads without deforming. The exact propertiesand dimensions are adapted to the defined requirements.

The two inclined surfaces 3, 4 are in one embodiment symmetrical withrespect to a radial centreline 7 of the locking device. Thus, the secondinclined surface 4 is in this example a mirror image of the firstinclined surface 3. The first inclined surface 3 comprises a startingpoint 10 and an end point 11. The second inclined surface 4 comprises astarting point 15 and an end point 16. The inclined surface between thestarting point 10, 15 and the end point 11, 16 is preferably straight,but slightly concave or convex surfaces are also conceivable, as long asan appropriate locking action can be achieved. The inclined surface issuitably shaped in an axial direction to fit the geometry of the rollerelement used. If the roller element is a ball, the inclined surface ispreferably provided with a groove or the like in order to hold the ballin an axial manner and also to better distribute the load from the ballto the inclined surface. If the roller element is a cylinder, theinclined surface is preferably straight in the axial direction and issuitably adapted to fit the roller element.

The starting point 10 is positioned at the distance a from the radialcentreline 7. The distance a is preferably smaller than half of thediameter of the roller element. In this way, a central section 9 betweenthe starting points of the two inclined surfaces is obtained. In oneembodiment, the central section 9 is an opening that preferably issmaller than the roller element. The roller element will thus bear onthe starting points of the inclined surfaces when the roller element isin a released state. The size of the central section 9 can also belarger that the roller element. In this case, another retaining means isused to retain the roller element in the locking device. The centralsection 9 may also be a section connecting the starting points of theinclined surfaces. The central section is in this case provided with arecess wherein the roller element will rest when the roller element islifted, i.e. when the locking device is in a released state. Dependingon the material used in the inclined surfaces, it may be advantageous touse another material in the central section. If the inclined surfacesare made of steel and the lifting device is an electromagnet, thecentral section is preferably made of a non-magnetic material, such asplastic or a non-magnetic metal. The advantage of having a centralsection connecting the starting points is that the locking device willbe shielded, which will improve the reliability. The central section mayalso be incorporated with the lifting device.

The starting point 10 is positioned at a distance b from the centre axis8 of the locking device. The end point 11 is positioned at a distance cfrom the centre axis 8 of the locking device. The distance b is largerthan the diameter d of the roller element added to the radius r of theaxle to which the locking device is adapted to be mounted. Thus, thedistance from the starting point 10 to the axle surface 13 is largerthan the diameter d of the roller element. The distance c is smallerthan the diameter d of the roller element added to the radius r of theaxle to which the locking device is adapted to be mounted. Thus, thedistance from the end point 11 to the axle surface 13 is smaller thanthe diameter d of the roller element. The distance between the inclinedsurface 3 and the axle surface 13 will decrease in the direction towardsthe end point 11.

FIG. 2 shows a locking device mounted to an axle 12. The centre axis 8of the locking device is mounted so that it coincides with the centreaxis of the axle. When the roller element 2 is held in the centralsection 9 with a lifting device 6, the axle is free to rotate and theroller element is not in contact with the axle surface 13. This state iscalled the released state.

When the lifting device is disengaged, the roller element will be pusheddown towards the axle surface by the spring element 5. The rollerelement will in this case be forced to bear on the axle surface 13, asis shown in FIG. 3. When the axle rotates, the roller element will beforced to follow the rotational direction of the axle. In this example,the rotation is in the counter-clockwise direction as indicated by arrow14. Due to the rotation, the roller element will be forced in thedirection towards the end point 11. Since the distance between theinclined surface 3 and the axle surface 13 decreases in this direction,the roller element will be squeezed between the inclined surface 3 andthe axle surface 13. The friction between the roller element and theinclined surface will prevent the roller element from rotating, and thefriction between the roller element and the axle surface will preventthe axle from rotating. The axle is thus in a locked state as shown inFIG. 4.

The surface of the inclined surface, the roller element and/or the axlesurface may be treated in order to increase the friction of thatsurface. Such a treatment may be some kind of mechanical surfaceconditioning, such as etching, grinding or the like, or by applying afriction material to the surface, such as a plastic or rubber material.

When the axle is locked, or when the roller element is engaged in orderto lock the axle, it is of advantage to, at the same time, disengage ordecrease the driving power applied to the motor. In this way, damage tothe motor, the gear box and/or the device driven by the motor can beavoided. One way of detecting when the axle is locked is to monitor thecurrent applied to the motor. A current sensing device measures thecurrent through the motor. When the motor is blocked, i.e. cannotrotate, the current consumption of the motor will increase. When thecurrent increases rapidly, preferably in connection with the engagementof the roller element, i.e. disconnection of the power to the liftingdevice, the axle will be in the locked state. This detection method issuitable when the drive current and the blocking current for the motordiffers enough, e.g. by a factor 2 or more.

Another way of detecting a locked axle is to use a rotational sensorthat measures the rotation of the motor. When the sensor indicates thatthe rotation of the motor is stopped, preferably in connection with theengagement of the roller element, the axle will be in the locked state.

This type of locking action of the axle has the advantage that it ispassive, i.e. there is no power requirement of the locking device tokeep the axle in a locked state. The locking action will thus beself-powered and will not release by itself.

Depending on the mounting position of the locking device, the springelement 5 may not be necessary. If the locking device is positioned suchthat gravity will pull the roller element onto the axle surface, thespring element may be omitted. For most applications, where the lockingdevice or a motor with a locking device may be positioned in anyarbitrary position, a spring element 5 will ensure that the rollerelement will be in contact with the axle surface when the roller elementis in the engaged state.

In order to release the axle from the locked state, i.e. to unlock theaxle, the motor is rotated somewhat in the opposite direction. In theexample described here, the motor will be rotated in the clockwisedirection. At the same time, the power to the lifting device is applied.When the motor is reversed, the roller element will be forced out of thelocked state and will rotate on the axle surface towards the centralsection. When the roller element is released from the locked state, itwill be attracted by the lifting device and will thus be lifted from theaxle surface to the released state. When the roller element is in thereleased state, the motor can be rotated in any direction and the devicedriven by the motor can be driven to the required position.

The spring element 5 is in this example a flat blade spring, but otherspring elements can be used as well. These may include different typesof springs or other resilient elements, such as rubber or plastic. Thespring element is dimensioned so that the roller element will be pushedtowards the axle surface regardless of the mounting position of thelocking device, when the lifting device is not powered. When the liftingdevice is powered, the lifting device will overcome the force of thespring element so that the roller element is attracted towards thelifting device, regardless of the mounting position of the lockingdevice. The spring element will push the roller element against the axlesurface. In order to do this, the spring element may have to extendbelow the starting point 10. This may be done through apertures orrecesses in the locking device, or by positioning the spring element atthe end surfaces of the roller element.

The lifting device is preferably an electrically powered device, e.g. anelectromagnet. One advantage of using an electromagnet is that acontactless lifting device is obtained. The roller element 2, theinclined surfaces 3, 4 and the spring element 5 may be encased in orderto prevent debris or lose parts from entering the locking device. Evensmall contaminations may deteriorate the performance of the lockingdevice. By encasing the locking device and using an outer lifting deviceacting on the roller element through the encasing, a reliable lockingdevice is obtained. The electromagnet is positioned at the centralsection 9, close to the position in which the roller element rests whenit is in the released state.

The lifting device may also comprise a permanent magnet that isdisplaced mechanically between a position in which the roller element isattracted towards the permanent magnet and a position in which thepermanent magnet does not attract the roller element. The permanentmagnet can be moved between these two positions in different ways, e.g.by using a lever or a rotational element.

The locking device is preferably circular. FIG. 5 shows an embodiment ofa circular locking device, with a circular housing 17. The lockingdevice is placed around an axle and by using a circular locking device,a compact locking solution is obtained. The forces that are to be takenup by the locking device are distributed in an optimal way using acircular locking device. Depending on the use of the locking device,other shapes are also conceivable.

In a second embodiment of the invention, the locking device isresiliently suspended to the mechanical device incorporating thecylindrical element. This may e.g. be a motor with an axle as thecylindrical element. The resilient means that suspend the housing (notshown) may be springs, a rubber or plastic material or the like.Preferably, the resilient means are relatively stiff. In the engagedstate, as shown in FIG. 5, the resilient suspension will position thelocking device symmetricaly around the axle, as in the examples shownabove for the fixedly attached locking device.

FIG. 6 shows the locking device according to the second embodiment in alocked state. When the roller element 2 is pressed towards the axle bythe spring element 5, and the axle 12 rotates in the direction shown byarrow 14, the roller element will roll on the axle and move towards theinclined surface 3. When the roller element touches the inclinedsurface, the roller element will push the inclined surface, and thus thehousing, away from the axle surface 13, since the housing is resilientlysuspended. The housing will stop when the inner surface 18 of thehousing bears on the axle surface 13. This action will put the lockingdevice in a locked state. In this embodiment, the brake area acting onthe axle is greater than in the first embodiment, since the axle isprevented from rotation not only by the roller element area but also bythe area between the axle and the inner surface 18 of the housing.

Since the housing is resiliently suspended, it is of importance that thehousing, and thus the locking device, is rather fixedly positioned in arotational manner. Otherwise, the complete locking device will rotatearound the axle which would at least make the rotational play greater.One way to prevent the locking device from rotating but still allow thelocking device to be resiliently suspended is to mount the lockingdevice on a hinge pin 19. The hinge pin will prevent the locking devicefrom rotating, but will allow the locking device to pivot slightly sothat the inner surface of the housing can bear against the axle when thelocking device is in the locked state.

In one development of the locking device, a detection means is used todetect when the roller element is in the released state. Such adetection means may be a switch that is toggled by the roller elementwhen it enters the released state. It may also be an optical sensor thatdetects when a light beam is interrupted by the roller element. When thelifting device is an electromagnet comprising a coil, it is possible tomeasure the induction in the coil. The induction will differ when theroller element is close to the coil compared to when the roller elementis in a locked position. This method is simple and reliable, since abroken switch may give the same signal as when the roller element is inthe released state.

By detecting that the roller element is in the released state after ithas been released from the locked state, the power can be applied to themotor without any risk of damaging the motor or the locking device. Thiscould be the case if the roller element was not in the released stateeven though it was released from a locked state. Applying power to themotor when the roller element is in the engaged state, rolling on theaxle surface, will force the roller element into a locked state again.

In an embodiment of the locking device, the locking device is providedwith detection means to detect in which locked state the roller elementis. The roller element is in a first locked position when the rollerelement is trapped between the first inclined surface 3 and the axlesurface and in a second locked position when the roller element istrapped between the second inclined surface 4 and the axle surface. Bydetecting in which locked position the roller element is, the rotationaldirection in which to drive the motor in order to release the rollerelement can be decided.

When the motor is provided with a rotational sensor, the detection ofwhich locked position the roller element is in can be done by measuringthe rotational direction of the motor when the axle locks. A controlunit connected to the sensor and driving the motor can store the lastdirection of the motor and will thus know in which direction to drivethe motor in order to release the locking device. By using therotational sensor information, the control unit can also selectivelydrive the motor the required rotational angle in order to release thelocking device. The rotational angle to release the locking device willdepend on the geometry of the locking device, but may e.g. be in therange of 5 to 15 degrees for the described example. If the motor is tobe rotated in the direction it was rotating when the axle was locked, asmall reverse rotation will release the locking device and the motor canthen be rotated in the desired direction. This will enable a more orless play free operation of the motor. With a gear ratio of the systemdriven by the motor, the play will be further reduced.

One application in which the locking device may be used is a linearactuator. An electrically powered linear actuator is provided with amotor. Some linear actuators, e.g. the types using a sliding screw ornut, may be self-locking when the motor is disengaged. Some types, e.g.the ones provided with a screw or nut using balls or rollers, may havesuch a low internal friction so that they are not self-locking. Thelocking device according to the invention is suitable for these types.Linear actuators of this kind may be either of the type having a motormounted at one end of linear actuator, i.e. at a rear end of the screwor longitudinal nut, or of the type where the motor is mounted aroundthe screw or longitudinal nut. The locking device according to theinvention is suitable for both types.

The motor may be driven by an external control unit. The control unitmay be any kind of suitable control unit, such as an analogue or digitalcontrol unit. The linear actuator may have a standard PLC compatibleI/O-interface using discrete signal lines or may have an integratedstandard fieldbus interface. Most commonly, a standard PLC compatibleI/O-interface will be used for the communication between the motor andthe control unit may. Two signal lines can be used for the commands“clockwise rotation” and “counter-clockwise rotation”. These signals maybe either low-level, when a separate power connection is provided, orhigh level, when the signals is used to drive the motor directly. Thisinput signal may also comprise information of the motor speed, i.e. howfast the motor should rotate. Depending on the type of motor, a voltagesetting the speed or a modulated signal may be used as input signal.

In a further embodiment of the invention, the locking device comprises asecond roller element, a second set of inclined surfaces, a secondspring element and a second lifting device (not shown). This second setof locking elements is preferably arranged at the side of the axleelement opposite from the first set of locking elements, i.e. in asymmetrical manner. The second roller element is used in parallel withthe first roller element 2, i.e. the two roller elements are releasedand engaged at the same time. One advantage of using two sets of lockingelements is that a symmetric load on the axle element is obtained, whichwill reduce wear on the axle element, bearings etc. caused by an unevenload. Another advantage is that the total load which the locking devicecan handle may be increased. The second set of locking elements ispreferably identical to the first set of locking elements. A furtheradvantage of using a second set of locking elements is that the securityof the locking device increases, should one roller element fail toengage for some reason.

In a further embodiment, the locking device comprises more sets oflocking elements, positioned symmetrically around the axle element. Thismay be advantageous for axle elements with larger diameters, in order toincrease the total force that the locking device can handle. Dependingon the size of the axle element and the load carried by that axleelement, typically three or four sets of locking elements positionedaround the axle element may be appropriate.

In a further embodiment of the inventive locking device, the axleelement 12 is provided with an outer tubular element (not shown). Thistubular element is attached to the axle element, so that the outersurface of the tubular element acts as the contact surface for theroller element. The tubular element may be a ring shaped element with awidth approximately the same as the roller element or may be a longertubular element. The tubular element is attached to the axle elementwith some type of friction coupling.

The friction coupling can be e.g. a mechanical clamp with a predefinedclamping force that allows the tubular element to slip on the axleelement if a force larger than a predefined force is applied to the axleelement when the roller element is engaged. The friction coupling mayalso comprise a breakpin or the like that will break at a predefinedload, allowing the tubular element to slip with a predefined frictioncoefficient. This will prevent the locking device and/or the axleelement from being damaged if an excessive force is applied to thesystem. The friction coupling can also comprise a friction materialapplied between the axle element and the tubular element. The frictionmaterial will connect the axle element and the tubular element in afixed manner when the applied force is below a predefined value, butwill allow the tubular element to slip on the axle element when a largerforce is applied. The friction material may be a rigid friction materialsuch as the material used in brake linings, or may be a rubber orcompound that slips or becomes viscous at a predefined load and/ortemperature.

One purpose of the friction coupling is to prevent an overload on thelocking device. Another purpose is to provide a brake function. This isespecially advantageous if the roller element is engaged when the axleelement is rotating at a high speed. Such an engagement action may beperformed inadvertently if part of the system does not function properlyand an engagement at a high speed is thus allowed, or may be performedas a security stop if a malfunction is detected somewhere in the systemand an emergency stop is required. With the friction coupling, acontrolled emergency stop can be performed without breaking themechanical system.

The invention is not to be regarded as being limited to the embodimentsdescribed above, a number of additional variants and modifications beingpossible within the scope of the subsequent patent claims.

REFERENCE NUMERALS

-   1: Locking device-   2: Roller element-   3: First inclined surface-   4: Second inclined surface-   5: Spring element-   6: Lifting device-   7: Radial centreline of locking device-   8: Centre axis of locking device-   9: Central section-   10: Starting point of first inclined surface-   11: End point of first inclined surface-   12: Cylindrical element-   13: Cylindrical surface-   14: Rotational direction-   15: Starting point of second inclined surface-   16: End point of second inclined surface-   17: Housing-   18: Inner surface of housing-   19: Hinge pin-   a: Distance between starting point and radial centreline-   b: Distance between starting point and centre axis-   c: Distance between end point and centre axis-   d: Diameter of roller element-   r: Distance between cylindrical surface and centre axis

1. A locking device to rotationally lock a rotatable cylindricalelement, the locking device comprising: a roller element having adiameter, and a body having an inclined surface with a starting pointand end point, the locking device being positionable in relation to acylindrical surface extending about the cylindrical element such that adistance between the starting point of the inclined surface and thecylindrical surface is greater than the diameter of the roller elementand a distance between the end point of the inclined surface and thecylindrical surface is lesser than the diameter of the roller elementsuch that the roller element is releasably engageable with the inclinedsurface and with the cylindrical surface to prevent rotation of thecylindrical element, means to selectively position the roller elementwith respect to the cylindrical surface.
 2. The locking device accordingto claim 1, wherein the locking device has a radial centreline, theinclined surface is a first inclined surface, and the locking devicefurther comprises a second inclined surface with a starting point and anend point, the second inclined surface being positioned opposite fromthe first inclined surface relative to the radial centreline andpositioned in relation to the cylindrical surface such that a distancebetween the starting point of the second inclined surface and thecylindrical surface is greater than the diameter of the roller elementand a distance between the end point of the second inclined surface andthe cylindrical surface is lesser than the diameter of the rollerelement.
 3. The locking device according to claim 2, wherein the firstand second inclined surfaces are symmetrical about the radialcentreline.
 4. The locking device according to claim 1, wherein themeans to selectively position the roller element with respect to thecylindrical surface is a lifting device, the lifting device beingactivateable to lift the roller element from the cylindrical surface inorder to place the locking device in a released state.
 5. The lockingdevice according to claim 4, wherein the lifting device is a magnet. 6.The locking device according to claim 5, wherein the lifting device isan electromagnet.
 7. The locking device according to claim 4, whereinthe locking device further comprises a spring element configured to biasthe roller element towards the cylindrical surface when the liftingdevice is disengaged.
 8. The locking device according to claim 1,wherein the locking device further comprises means to detect when theroller element is in a lifted state.
 9. The locking device according toclaim 1, wherein the locking device further comprises means to detect ifthe locking device is arranged in one of a first locked state and secondlocked state.
 10. The locking device according to claim 1, wherein theroller element is a ball.
 11. The locking device according to claim 1,wherein the roller element is a cylinder.
 12. The locking deviceaccording to claim 1, wherein the cylindrical surface is a surface ofthe cylindrical element.
 13. The locking device according to claim 1,wherein the cylindrical surface is a surface of a tubular elementcoupled to the cylindrical element by means of a friction coupling. 14.The locking device according to claim 1, further comprising a hinge pin,the locking device body being pivotable upon the hinge pin.
 15. Thelocking device according to any claim 1, wherein the locking devicefurther comprises a second roller element, second means to selectivelyenable the second roller element to be distanced from the cylindricalsurface, and an additional inclined surface.
 16. The locking deviceaccording to claim 15, characterized in that the locking device furthercomprises at least a second additional inclined surface, the secondadditional inclined surface being positioned opposite from the firstadditional inclined surface relative to a radial centreline of thelocking device.
 17. (canceled)